The substituted phenols, especially the derivatives with a 4-alcoxy substituent, are important substances in organic chemistry because they are intermediate products for the manufacture of medicines, agrochemicals and dyes. They are useful as polymerization inhibitors for vinyl-type monomers and polyester stabilizers as well as antioxidants for food and cosmetics also. There is considerable interest due to the synthesis of such products in industry and academy. See, for example Caproiu, M. T.; Banciu, A. A.; Olteanu, E. RO 105090, 1994; Saito, T.; Hirayama, T.; Sakagushi, S. JP 08151343, 1996; Schwabe, K.; Redslob, J.; Breitfeld, D.; Zeisig, R.; Tschiersch, B.; Wohlrab, W.; Wozniak, K. D.; Bayer, C.; Nowak, C.; et al. DD 287482, 1991. A strategy for the synthesis of these phenols consists in the Baeyer Villiger reaction with the corresponding aldehydes (Krow G. Org. React. 1993, 43, 251).
In general, this reaction is carried out using organic peracids as oxidizing agents. Meta-chloroperbenzoic acid (Godfrey, I. M.; Sargent, M. V.; Elix, J. A. J. Chem. Soc. Perkin Trans. 1 1974, 1353–1354.), as well as monopersuccinic acid (Anoune, N.; Hannachi, H.; Lanteri, P.; Longeray, R.; Arnaud, C. J. Chem. Ed. 1998, 75, 1290–1293.) gave good to excellent yields of the corresponding phenol in the case of the ortho-anisaldehyde and the para isomer. The meta-anisaldehyde transforms predominantly into meta-anisic acid. The disadvantage of an organic peracid like oxidizer is that it implies high costs and safety measures during its storage and handling, and produces at least a molecule of acid as waste product.
Oxygenated aqueous water would be a good oxidizing agent since it is safer and produces only water as sub-product. Nevertheless, it is not sufficiently reactive and needs activation by a catalyst. Activation may be achieved by selenium catalysts, and thus 4-methoxyphenol may be obtained from the corresponding aldehyde with an excellent yield (Syper, L. Synthesis 1989, 167–172). Nevertheless, in this case considerable quantities of catalyst are necessary, which have to be recovered and recycled or rejected, since only 12 cycles per active centre per 30 hours of reaction time are obtained.
The oxidation of aldehydes with H2O2 may also be catalyzed by Bronsted acids. The oxygenated water, activated by the sulphuric acid in methanol as solvent produces 4-methoxyphenol with an excellent yield. Nevertheless, anhydrous conditions and highly concentrated oxygenated water are necessary for this since it is considered that the reaction goes ahead via the peroxyhemiacetal that is unstable in the presence or water (Matsumoto, M.; Kobayashi, H.; Hotta, Y. J. Org. Chem. 1984, 49, 4740–4741). These anhydrous conditions of the reaction lead to extra costs in safety measures since the concentrated oxygenated water is potentially explosive.
On the other hand, the oxidation of Baeyer Villiger with oxygenated water in formic acid is less suitable for the production of phenols since it has been developed for the general oxidation of aldehydes to carboxylic acids (Dodd, R. H.; Le Hyaric, M. Synthesis 1993, 295–297). The present invention has as its main aim to overcome the disadvantages of the above-mentioned method by means of a method wherein the use of oxygenated water as oxidizing agent and the use of catalysts that give high conversions and are easily recyclable is permitted and that, besides, allows by simply changing the conditions of reaction, the possibility to choose as main final product different products as for example aryl formiate or substituted phenol.